<<< In a message dated 10/2/1999 10:40:18 PM Eastern Daylight Time,
Chuck Kuecker writes: <<Speaking as one who actually tried building a wireless stun gun, I have two comments about the 'UV laser' approach: First, any laser powerful enough to ionize air is a weapon all in itself. Even if it was only breifly pulsed, it takes quite a bit of energy to ionize a column of air. Second, to maintain the ionized channel long enough to conduct current will take a large voltage to strike the plasma arc, and a large discharge current to keep it lit. I doubt it will be possible to send the 'T-wave' pulses as used in the original Taser product through this channel - it will be more like a lightning bolt. Also, the fact that a return path is required would either put the operator at risk in becoming part of the circuit, or would require two ionized paths, parallel to each other and fairly close together. What's to keep the current from taking the easy way out and arcing right at the projector? Before patent research found that I had been scooped by Jaycor (check out their webpage for some really DUMB idea), I built and tested a stun gun using two conductive streams of water. Due to breakup of the streams, the best range I got was just over three feet - but I was able to light a neon target reliably at that distance. The obvious problems with this approach are that a raincoat completely defends against either conductive streams or any 'UV' approach that does not incinerate its' target.>> Thank you very much for your post, Chuck. Some hands on experience is exactly what we need here in our theoretical musings<g>. Your comments are the kinds of things I thought might be a problem with the wireless tasers (though they were quite muddled in the back of my head and I didn't have enough experience in this area to really be certain if there were anything
to
them). I was worried that it would take a lot of energy to successfully
fire
a taser without wires, and hadn't even considered the two pathway issue.
And
of course the fact that it is easy to foil a taser with relatively common clothes protection is a problem as well. Too bad that the UV laser would require so much energy (thus increasing its destructive capability). Glen Finney >>>

Yeah, I'm replying to my own post<g>.

Found some papers on this guy Herr's concept of a UV laser taser, which they
are claiming will be able to create an ionized channel of air without doing
significant harm to the body (effects on eye seem to be brought up). Check
out the patent and some of the articles on the proposed weapon. Sounds like
there is still a lot of work to be done, but does the physics add up? Anyone
have any hard data on what it takes to sufficiently ionize the air for
something like this to work?

These and other objects are achieved by transmitting relatively high
frequency electrical impulses to the target by means of one or two
electrically conductive channels of ionized air produced within one or two
beams of intense ultraviolet radiation aimed at the target, and by placing a
high-voltage field of the opposite polarity across the path of each beam.

The present invention functions by immobilizing the target person or animal
at a distance. It performs this function by producing skeletal muscle
tetanization in the target subject. Tetanization is the stimulation of muscle
tissue by a series of electrical impulses of such frequency as to merge
individual muscle contractions into a single sustained contraction. The
immobilizing tetanization is maintained as long as the weapon continues to
produce an electrical current within a major portion of the skeletal
musculature of the subject, and for a brief time thereafter due to paralysis
caused by the temporary inhibition of neuromuscular impulses. The optimum
current and frequency required to create and maintain immobility while
avoiding impairment of cardiac or respiratory activity are 25 milliamperes
and 100 hertz, respectively. Currents in the range of 20 to 50 milliamperes
and 5 to 2500 hertz may also be employed, with the higher frequencies
requiring higher currents. A frequency of about 2 hertz may ultimately be
used to produce painful spastic contractions. A minimum electrical potential
of approximately 600 volts is required to overcome skin resistance without
producing burns.

The most effective current waveform in producing tetanization is that which
most closely duplicates the physiologically produced neural impulse. As
Offner points out, this waveform is an exponentially rising pulse. The second
most effective waveform is a square wave, whereas the least effective is a
sine wave. Due to their rapid risetimes, square waves allow the greatest
penetration through the clothing and skin of the target subject.

Further, the differences in the effectiveness of various waveforms constitute
an inherent safety factor in the operation of the instant weapon. This safety
factor is a result of the rapid absorption by biological tissue of the
harmonic frequencies within complex waveforms such as square waves. A 20 to
50 milliampere current is thus able to stimulate only the target subject's
skeletal muscles, and cannot penetrate to the autonomically-controlled
internal muscles such as the heart.

A lethal variation of the present weapon could be implemented by increasing
the current above approximately 250 milliamperes. A sine wave current having
a density of about 5 milliamperes per square centimeter that flows through
cardiac muscle for more than about two seconds may initiate ventricular
fibrillation. The duration of the current needed to cause ventricular
fibrillation is inversely proportional to the current density within the
cardiac muscle.

The current carried by the ionized air channel is limited by the number of
free electrons within the ultraviolet beam. A minimum 20 milliampere current
required to induce skeletal muscular tetanization can be carried by a gaseous
channel with a concentration of 10.sup.8 ions per cubic centimeter. This
concentration is most efficiently achieved in air by ionizing molecular
oxygen with coherent or columnated incoherent ultraviolet radiation having a
wavelength of 193 nanometers. Shorter wavelengths may be employed as optical
technology progresses.

At its normal operating intensity and a wavelength of 193 nanometers, the
ultraviolet beam is safe to the skin because it cannot produce more than mild
erythema akin to a sunburn unless it is directed at the same location for
many minutes. Moreover, it is safe to the eyes because wavelengths near 193
nanometers cannot penetrate the cornea to reach internal ocular structures
such as the lens and retina.

At this wavelength, molecular oxygen has a two-photon ionization cross
section of 1.times.10.sup.-34 cm.sup.4 /watt. Because of its low ionization
threshold, the number of photons required for ionization, and its large
proportion in the atmosphere, it is easily able to create sufficient electron
density.

The most efficient source of 193-nanometer radiation presently available is
the argon fluoride discharge-pumped excimer laser. A reasonable power
density, pulse duration, and pulse repetition rate for this laser is 5
megawatts per square centimeter, 10 nanoseconds, and 200 pulses per second,
respectively.

An argon fluoride laser with an aperture of 1 square centimeter has a power
density (energy output) of 10 millijoules per pulse or 1 megawatt per square
centimeter. Each pulse liberates 6.3.times.10.sup.6 electrons, or
6.3.times.10.sup.14 electrons per second in the air immediately outside the
aperture. A power density of 50 millijoules per pulse or 5 megawatts per
square centimeter liberates 1.6.times.10.sup.8 electrons during each pulse,
which is equivalent to 1.6.times.10.sup.16 electrons per second.

A narrow beam of ultraviolet radiation may also be generated from the
collimated emission of an ultraviolet lamp.

The electron density in the channel of ionized air is a function of the ratio
between the electron production and loss rates. In both the two-body and
three-body electron attachment processes, the delay time between the end of
the laser pulse and the beginning of the high-voltage tetanizing pulse
determines the number of available electrons. When the electron energy is
only 0.1 electron volt, for example, the three-body attachment is rapid, and
the steady-state electron density for a 193 nanometer, 5 megawatt per square
centimeter beam falls to 8.times.10.sup.7 per cubic centimeter.

The range of the present weapon is determined by the rate at which the laser
beam is absorbed by the atmosphere. A 193-nanometer wavelength beam is
attenuated in dry air at about 1.times.10.sup.-4 per centimeter. It will thus
propagate approximately 100 meters before its intensity is decreased to 1/e
of its initial value. As a consequence, the 1.6.times.10.sup.8 electron
density at the aperture of an argon fluoride laser with a power density of 5
megawatts per square centimeter falls to 2.2.times.10.sup.7 after 100 meters.
Because the minimum electron density required to transmit a current is
between 10.sup.6 and 10.sup.8 per cubic centimeter, the above ionized channel
should conduct the tetanizing current at least 100 meters. The range of this
weapon could be increased, however, by the use of a more efficient
ultraviolet source.

Various techniques, including those suggested in U.S. Pat. No. 4,017,767 Ball
and U.S. Pat. No. 5,175,664, Diels et al. which are incorporated herein by
reference, may be used in order to enhance the multi-photon and collisional
ionization along the laser beams. These techniques are well known to persons
skilled in the electrical arts.>>